1. Field of the Invention
The present invention relates to a load detecting apparatus used for detection of various loads, such as a depression load of the vehicle pedal and the like, a cable tension of the vehicle parking brake, and a seat load of the vehicle seat.
2. Discussion of Related Art
A conventional load detecting apparatus for the above detection has a structure shown in FIG. 9 to FIG. 11. FIG. 9 is a perspective view of the conventional load detecting apparatus, FIG. 10 is a developed view of a strain body in the above load detecting apparatus, and FIG. 11 is a circuit diagram of the above load detecting apparatus. In FIG. 9 to FIG. 11, the load detecting apparatus includes a hollow cylindrical strain body 1, a pair of circumferential strain detecting elements 2, a pair of axial strain detecting elements 3, a power source electrode 4, a GND electrode 5, an output electrode 6 and the like.
That is, on an outer peripheral surface of the hollow cylindrical strain body 1 in which strain occurs receiving the load, a pair of circumferential strain detecting elements 2 and a pair of axial strain detecting elements 3 both detecting the strain on the strain body 1 are provided. Also on the outer peripheral surface of the hollow cylindrical strain body 1, a power source electrode 4, a GND electrode 5 and an output electrode 6 are provided, which are electrically connected with the paired circumferential strain detecting elements 2 and the paired axial strain detecting elements 3 by a circuit pattern 7. Thus, a bridge circuit shown in FIG. 11 is constructed.
The conventional load detecting apparatus thus constructed is used in a state where a load (compression force) is applied to the hollow cylindrical strain body 1 parallel to an axis C thereof. That is, when the compression force is applied in parallel to the axis C of the strain body 1, the strain occurs in the deformed strain body 1, and a resistance value of the axial paired strain detecting elements 3 decreases, while a resistance value of the paired circumferential strain detecting elements 2 increases. The paired axial strain detecting elements 3 and the paired circumferential strain detecting elements 2, constructing the bridge circuit together with the power source electrode 4, the GND electrode 5, the output electrode 6 and the circuit pattern 7, outputs the output signal (voltage) corresponds to the compression force applied to the strain body 1 from the output electrode 6. As the well-known document disclosing such load detecting apparatus, a following patent document 1 (Japanese Patent Application Laid-open No. H6-2078660 can be illustrated.
However, the above load detecting apparatus has a construction such that the load is applied to the strain body 1 parallel to the axis C thereof, and accordingly a compress strain occurs in the strain body. Whereas, the hollow cylindrical strain body hardly deforms by the compression force in the direction of the axis C, so that there is a limit of magnitude of the compression strain detected. Thus, the paired axial strain detecting elements 3 and the paired circumferential strain detecting elements 2 can hardly detect the strain. As a result, sensitivity of the output signal outputted from the output electrode 6 is lowered.
The present invention is made in view of the above mentioned circumstances and therefore has an object to provide the load detecting apparatus in which the strain body can be easily deformed by the load applied thereto, so that the sensitivity of the output signal increases.